Bloodstream infections are associated with high morbidity and mortality, yet current diagnostic methods of culture, followed by biochemical identification and antibiotic susceptibility testing, can take several days to perform. Typically, empiric therapy is initiated based on clinical symptoms, and test results only impact clinical decisions when the initial therapy fails. The ability to characterize bloodstream infections within the first hour after a positive blood culture result would significantly boost the clinical relevance of the diagnostic information provided. Molecular amplification methods have been proposed to fill this need, but serious challenges to this approach remain. The positive blood culture broth itself represents a naturally amplified population of microorganisms with potential for use in a variety of rapid identification (ID) tests.
Methicillin-resistant Staphylococcus aureus (MRSA) is a dangerous community- and hospital-acquired pathogen that can rapidly cause infection even in healthy patients. It is also commonly present as normal flora on a number of elderly and sick patients, and has the ability to quickly cross-infect multiple patients in a health care environment. The mechanism of “methicillin resistance” is substantially mediated by the production of an altered penicillin binding protein 2, known as PBP2a, which retains functional enzymatic activity but has a significantly reduced affinity for beta-lactam antibiotics. Vancomycin-resistant enterococci (VRE) is another dangerous group of pathogens requiring immediate identification. In a manner similar to methicillin resistance, vancomycin resistance is also mediated by a reduced affinity of the antibiotic to it's cell membrane target.
Current methods to identify MRSA and VRE are labor-intensive and potentially unsafe due to steps that can result in aerosol exposure to the user. Rapid, yet safe and reliable methods are urgently needed to isolate microorganisms contained in blood culture broth that are compatible with rapid determination of resistance. Such methods are provided by the present invention.